Page:Mind (New Series) Volume 12.djvu/487

III. THE PHYSIOLOGICAL FACTORS OF THE ATTENTION-PROCESS (III.). BY W. MCDOUGALL. MUSCULAK ACTIVITY AS A FACTOK OF THE ATTENTION- PEOCESS. THAT motor activities play a part of some importance in the attention-process is now pretty generally admitted, and this general statement needs no further proof. But I have to report in this section some observations that seem to afford more direct evidence of this influence than has yet been pro- duced and to throw some light upon the way in which this influence is exerted. Most of the experiments to be described in this and the following sections deal (1) with the phenome- non described by me in a former paper l and there called ' the complete fading of visual images ' ; (2) with the fadings and reappearances of after-images ; (8) with the alternations of colours and contours in the struggle of two different visual fields presented to the two eyes ; (4) with the alternations of different modes of perception of ambiguous figures such as those reproduced in figures 7 and 8 on pages 482 and 483 and in figure 2 of the first part of this paper. 2 It will probably be said by any reader, who may have had the patience_^o_follow my disquisition up to this point, that these phenomena, witF the Exception of those of the last group, have little or nothing to do with Attention. I will therefore indicate at once the general purpose of my observa- tions and the line of the argument that I found upon them. These four groups of phenomena have one striking feature in common, namely, that while the physical stimuli affecting the sense-organ remain unchanged or undergo only slow and gradual changes, the affections of consciousness to which they give rise undergo very marked and rapid changes. My 1 MIND, No. 37. 2 MIND, No. 43, p. 335.